Move CPP_PROLOGUE and CPP_EPILOGUE to the .cpp

This lets us avoid having to specify them in every C file.

include/jemalloc/internal/jemalloc_preamble.h.in

@@ -1,16 +1,6 @@
 #ifndef JEMALLOC_PREAMBLE_H
 #define JEMALLOC_PREAMBLE_H
 
-#ifdef __cplusplus
-#  define CPP_PROLOGUE extern "C" {
-#  define CPP_EPILOGUE }
-#else
-#  define CPP_PROLOGUE
-#  define CPP_EPILOGUE
-#endif
-
-CPP_PROLOGUE
-
 #include "jemalloc_internal_defs.h"
 #include "jemalloc/internal/jemalloc_internal_decls.h"
 
@@ -182,6 +172,4 @@ static const bool have_percpu_arena =
 #endif
     ;
 
-CPP_EPILOGUE
-
 #endif /* JEMALLOC_PREAMBLE_H */